The invention relates to improved coatings for metal substrate for exterior building products and to fluorocarbon solvent-borne primers and topcoats. In the manufacture of exterior building products, fluorocarbon-containing topcoats have become desirable due to their exterior durability with respect to chalk resistance and color retention. Acrylic resins, both thermoplastic and thermoset, add a measure of corrosion resistance to such coatings. As these components are varied in the topcoat it becomes necessary to modify the primer coat accordingly. Various approaches have been made to produce primers for use in conjunction with fluorocarbon topcoats. Polymers dispersed in organic solvents are disclosed in U.S. Pat. Nos. 3,340,222 and 3,324,069. Stoneberg (U.S. Pat. No. 4,314,004) teaches a process for using a pigmented, high fluorocarbon resin with an acrylic resin as an undercoat to a clear fluorocarbon/acrylic topcoat. U.S. Pat. No. 4,297,447 (Yasuda) teaches flexible coatings having a fluorocarbon in combination with (a) a thermosetting resin from the group epoxy resin, alkylphenol resin and polyurethane resin and with (b) a rubbery elastomer from the class of nitrile rubber, chloroprene rubber and thermoplastic polyurethane rubber. U.S. Pat. No. 4,379,885, (Grunewalder and Miller), similarly use primer compositions consisting essentially of polyepoxide resin in conjunction with an acrylic and fluorocarbon resin. Vasta (U.S. Pat. Nos. 3,784,506 and 3,859,123) teach polyvinylidene coatings based on epoxy and aminoplast resin. Abel (U.S. Pat. No. 4,383,075) teaches aqueous thermoset coatings comprising fluorocarbons, hydroxyl or carboxyl containing high Tg acrylics and melamine resin crosslinkers.
As seen by the above citations conventional fluorocarbons generally contain substantial amounts of epoxy resin in combination with the fluorocarbon and acrylic resin. While providing excellent durability, the art compositiom on have several disadvantages such as poor corrosion resistance, excessive ultra-violet transmission, and poor intercoat and substrate adhesion. In addition and for economy purposes, a process which eliminates the primer bake-cure step is desired. Such disadvantages have now been overcome by the non-epoxy containing fluorocarbon compositions of the present invention which can be applied as a primer or topcoat in a wet-on-wet process.